1. Field of Invention
The present invention relates to an optical switch device that redirects a beam of light traveling in free-space along a first direction to a second direction. Further, the present invention is directed to a plurality of optical switch devices that form a free-space optical matrix crossconnect apparatus.
2. Description of Related Art
Modem communications companies now use fiber optic cables as the primary carrier for voice and data signals transmitted as light beams for ground-based communications networks. Similar to communication networks using copper wire as the carrier for electronic signals, fiber optic cable trunk lines are interconnected to each other through switching nodes positioned at various locations throughout the service area of the communications network. Telephone calls, for example, are routed through nodes A, B and C. Occasionally, a communications failure may take place between nodes B and C. To restore communications, the signals which can no longer be routed through node C must be routed through an alternative node D. To achieve rerouting of the communications signals, a conventional free-space micromachined optical matrix switch is used. Also, conventional free-space micromachined optical matrix switches are used for signal routing passes for providing light signals to various locations.
One type of a conventional micromachined free-space optical matrix switch 2 is introduced in FIGS. 1-4. The conventional optical matrix switch 2 uses electrostatically actuated torsion mirrors 4. The optical matrix switch 2 includes a first base member 6 and a second base member 8. The first base member 6 has an array of bores 10 formed therethrough and arranged in a plurality of columns and rows.
As best shown in FIG. 3, the torsion mirror 4 has a reflective panel member 12 and a torsion bar 14 connected to the reflective panel member 12 by a connector section 16. One of ordinary skill in the art would appreciate that the reflective panel member 12, the torsion bar 14 and the connecting section 16 are formed as a unitary construction.
Each of the bores 10 is sized to receive a respective one of the torsion mirrors 4. Each of the torsion mirrors is mounted onto the first base member by embedding opposite distal ends 18 and 20 of the torsion bar 14 into the first base member 6 so that each of the torsion mirrors can pivot between a reflective state and a non-reflective state as explained in more detail below.
The second base member 8 includes an array of cavities 22 as best shown in FIG. 1. The first base member 6 and the second base member 8 are connected to each other with the cavities 22 disposed in a manner to receive an end portion of the reflective panel member 12 when the reflective panel member 12 is in the reflective state as shown by the torsion mirror 4 drawn in phantom in FIG. 4. A support wall 24 retains the reflective panel member 12 at an appropriate position for redirecting a beam of light L.sub.1 and L.sub.2 traveling in a first direction to a second direction.
As best shown by FIG. 1, the bores 10 and the associated torsion mirrors 4 are arranged in columns and rows labeled C1 and C2 and R1 and R2 respectively. Each of the bores 10 are sized to receive a respective one of the torsion mirrors 4. Electrical leads 28a-d provide electrical power to the respective ones of the torsion mirrors 4 at the torsion bar 14. In the non-reflective state, the reflective panel member 12 of the torsion mirror 4 is substantially disposed in a plane formed by a first base surface 30 of the first base member 6. The reflective panel members 12 located in R1, C1 and R2, C2 are shown in the non-reflective state whereby the light beams L.sub.1 and L.sub.2 pass underneath the torsion mirrors 4 as best shown by FIGS. 1, 2 and 4. In the reflective state, the reflective panel member 12 drawn phantomly in FIG. 4 is illustrated with an end portion of the reflective panel member 12 contacting the support wall 24. Also, the reflective panel members are positioned within the bores so that, for example, the light beams L.sub.1 and L.sub.2 being projected from the fiber optic cables 26a and b positioned in rows R1 and R2 are deflected by the reflective panel members located in R1, C2 and R2, C1 respectively so that the light beams L.sub.1 and L.sub.2 can be redirected to the fiber optic cables 26C and D located in C1 and C2 respectively. In brief, because each of the light beams in this example is redirected 90 degrees, a longitudinal axis "1" of the reflective panel member 12, as shown in FIGS. 2 and 3, must be oriented at a 45 degree angle .alpha. relative to the incoming and outgoing light beams L.sub.1 and L.sub.2 as best shown in FIG. 2.
For a more detailed explanation of the conventional optical matrix switch 2 described above, reference is made to Journal of Microelectromechanical Systems, Vol. 5, No. 4, December 1996 in an article entitled "Electrostatic Micro Torsion Mirrors for an Optical Switch Matrix" by Hiroshi Toshiyoshi and Hiroyuki Fujita. For additional details regarding conventional optical matrix crossconnects, reference is made to a book entitled "An Introduction to Photonic Switching Fabrics" by H. Scott Hinton, published in 1993 by Plenum Press in New York.
One problem with such an optical matrix switch described above is that a voltage must be continuously applied to retain the reflective panel mirror in the reflective state. Often, in practice, the torsion mirror may not be used for years before it is activated. Thereafter, it may continue to be used in the opposite state for another period of years. Thus, electrical power is being consumed while the torsion mirror is being retained in the reflective state. Also, another problem associated with the conventional optical matrix switch 2 is that precision alignment is required to connect the first base member and the second base member together so that the support wall 24 is properly oriented to retain the reflective panel member properly in its reflective state.
Additionally, electrostatic torque causes the reflective panel member to move between the reflective state and the non-reflective state. Electrostatic torque is a complicated area of the art and there is limited data to determine when mechanical fatigue might be expected over the lifetime of the conventional optical matrix switch. Also, switching from the non-reflective state to the reflective state requires approximately 300 milliseconds.